The present invention relates to a motorcycle particularly provided with an improved frame structure having a pair of main frame pipes arranged on both sides in a width direction of a motorcycle body.
A motorcycle provided with a known frame structure and structures associated therewith is shown in FIG. 5.
With reference to FIG. 5, a motorcycle has a frame A mainly composed of a head pipe B rotatably supporting a steering shaft and a pair of main frame pipes C, C fixed at front ends thereof to the head pipe B and extending rearward therefrom on both sides in a width direction of a motorcycle body. An air cleaner casing D is disposed between the main frame pipes C, C, and the surrounding of the air cleaner casing D is covered by a fuel tank. An engine unit E is suspended from the frame A at a portion below the air cleaner casing D, air-intake devices F, F, having leading end openings Fa, Fa inserted into the air cleaner casing D, are coupled with the engine unit E. The air-intake devices act to mix fuel jetted from an ignition means with an intake air from the air cleaner and supply the air/fuel mixture to the engine unit.
In the conventional structure of the motorcycle having paired main frame pipes mentioned above, it has been required for the frame A provided with the paired main frame pipes to be connected with each other by means of a coupling member for increasing the rigidity thereof against torsion or twisting motion applied thereto. However, in the structure mentioned above, because of the location of the air cleaner casing between the main frame pipes C, C, it was in fact impossible to arrange a coupling member therebetween. Of course, although it may be possible to locate the coupling member by eliminating a portion of the air cleaner casing interfering with the coupling member, in such arrangement, the capacity or volume of the air cleaner is reduced, resulting in a problem of lowering the intake performance.